Vehicles may include multiple axles coupled to wheels for supporting the weight of the vehicle on a surface. Some vehicles, such as locomotives, may include a front truck and a rear truck with two or more axles on each truck. One or more of the axles may be powered by a traction motor mounted on a truck frame, while one or more other axles may be unpowered. Axles may be mounted to the truck frame via one or more suspension assemblies for distributing the weight of the locomotive and trucks among the axles.
As the locomotive wheels apply tractive effort to the rails, the load on each axle may shift. In some examples, weight may transfer from a powered axle to an unpowered axle, thereby decreasing the normal force on the rail at the powered axle. Under these conditions, the possibility of wheel slippage at the powered axle may increase thus decreasing the tractive force of the corresponding wheels. It will be appreciated that such weight transfer may be at least partially the result of reaction forces applied by the truck frame to the traction motor mounted on the truck frame and coupled to the powered axle. It will also be appreciated that such reaction forces are created by the torque applied by the traction motor to the powered axle.
In some prior attempts to address such weight transfer issues, dynamic weight transfer systems that actively adjust the corresponding suspension have been used. Such systems, however, typically require additional actuators, linkages and/or other components to affect the dynamic weight transfer. Such additional components add undesirable packaging space requirements, complexity, and cost to the vehicle. In other examples, linear-acting, passive weight transfer systems may be utilized. However, such systems are typically effective only when tractive effort is applied in one direction. When the vehicle is moved in the opposite direction, the weight transfer functionality does not function to provide a net benefit.